Analyzing water resource projects for Southern California and Arizona

As prime contractor to the US Army Corps of Engineers, Los Angeles District, RDN prepared three economic analyses for water resource projects in Southern California and in Arizona. All were prepared in conformance with US Army Corps of Engineers guidance for National Economic Development (NED) account evaluations for civil works projects.

RDN’s first project was a reconnaissance-level economic analysis of flood control alternatives in the Tortolita Drainage Area in the Pima and Pinal Counties in Arizona. The Tortolita Drainage Area encompasses 154 square miles including nine drainage basins in an essentially undeveloped area northwest of Tucson. Rapid population growth in the region had increased the demand for buildable land, leading to proposed measures to enhance flood protection.  The purpose of this project was to identify and quantify the benefits and costs of six alternative flood control solutions in the drainage area. After compiling the best available planning information and local real estate development projects, RDN presented the annual benefits, costs, and benefit/cost ratios of each of the six alterative flood control solutions.

RDN’s second project was a feasibility-level flood inundation analysis of flood control alternatives for a portion of the Whitewater River Basin in Riverside County, California.  This study estimated flood-proofing savings due to development of a proposed flood control system.  We estimated expected annual inundation damages under without-project conditions over a 50-year period using the Hydrologic Engineering Center’s expected annual damage model.  In order to make such an appraisal we assessed existing development from county appraiser records, conducted a field survey to determine first floor elevations of the improvements, and prepared forecasts of future development based on the Riverside County General Plan, compilation of data from state and local agencies, and developer interviews.

RDN’s final project under this delivery order was preparing a feasibility-level study for how a proposed flood control project would affect recreational activities at the Hansen Dam Recreation Area in the City of Los Angeles.  Several recreation sites were more likely to become inundated with the proposed addition of a water conservation function.  To assess the differences among alternative water conservation plans, we forecasted future activity and then estimated the number of foregone visitor-days under each alternative based on the probability of inundation. Our analysis was used in determining the economic feasibility of the proposed project and in preparing the Environmental Impact Statement.